1. Field of the Invention
This invention relates to manufacturing synthetic fuels and petrochemicals. The invention more particularly relates to a process of expanding the product slate obtainable from the conversion of wet natural gas.
2. Description of the Prior Art
It is established that relatively low molecular weight aliphatic organic compounds, containing up to 8 carbon atoms in the longest hydrocarbon chain and containing at least one oxygen, sulfur or halogen heteroatom can be converted to very high quality gasoline boiling-range hydrocarbon materials. These heteroatom-substituted lower aliphatics are exemplified by alcohols, ethers, mercaptans, thioethers, carbonyls, thiocarbonyls, amines, amides and alkyl halides. The conversion of such heteroatom-containing materials to high quality gasoline boiling-range hydrocarbons is accomplished by contacting such materials alone or in admixture with each other in pure or impure state with a crystalline aluminosilicate zeolite catalyst having a silica to alumina mole ratio of at least about 12, a constraint index as defined below of about 1 to 12 and preferably a crystal density not substantially below 1.6 grams per cubic centimeter. Zeolite ZSM-5 is an example of such a catalyst. Conversion is typically accomplished at about 400.degree. to 1000.degree. F. Reference is made to U.S. Pat. Nos. 3,894,107; 3,894,106 and 3,907,915, the entire contents of which are incorporated herein by reference, including the references therein to illustrate zeolite catalysts.
Typical natural gas consists of hydrocarbons having a low boiling point. Methane makes up approximately 85 percent of the typical gas. Ethane is likely to be present in amounts up to 10 percent and propane up to 3 percent. Butane, pentane, hexane, heptane and octane may also be present. Whereas normal hydrocarbons having 5-10 carbon atoms are liquid at ordinary temperatures and pressures, these paraffins of higher molecular weight are present in natural gas in vapor form. Types of natural gas vary according to composition to result in a dry or lean (mostly methane) gas, wet gas which contains considerable amounts of the higher molecular weight paraffins, residue gas from which higher paraffins have been extracted and casing head gas which is derived from an oil well by extraction at the surface. Natural gas occurs in porous rock with or near accumulation of crude oil, and is always present to some extend wherever oil has been found.
In conventional processing, wet natural gas is subjected to a separation in which a C.sub.5.sup.+ fraction, called natural gas liquid, is removed leaving a residue gas which is then conventionally separated into a C.sub.1 /C.sub.2 dry gas fraction and a C.sub.3 /C.sub.4 LPG fraction.
It is conventional to convert the dry gas fraction to methanol or a mixture of alcohols. This is achieved by first steam reforming the dry gas portion of produce a synthesis gas. Steam reforming comprises reacting the dry gas portion with steam in the presence of a nickel catalyst in a closed reaction zone at a temperature within the range of about 1400.degree. to 1700.degree. F. and at a reaction zone pressure generally about 0 to 30 psiq. The product from steam reforming is a synthesis gas comprising carbon monoxide and hydrogen. The synthesis gas is then converted to methanol by passing the product gas over a methanol synthesis catalyst. Such a catalyst contains zinc and/or copper. Methanol synthesis operates at about 350.degree. to 600.degree. F. and 700 to 2500 psig. As noted above, processes have been developed for converting methanol or heteroatom-containing lower aliphatics to high quality gasoline. Thus, it has been known to convert the dry gas to high quality, highly aromatic gasoline by combining the preceding process steps.
It has further been proposed to increase the gasoline production from natural gas by converting more of the natural gas than just the dry gas portion to gasoline. U.S. Pat. No. 3,965,205 discloses a process in which C.sub.5.sup.+ natural gas liquids are mixed with methanol which has been formed from the dry gas portion and the mixture converted over ZSM-5 to gasoline. However, the product is limited to gasoline boiling-range hydrocarbons. It would be desirable to expand the slate of products which are derived from wet natural gas to include a wide slate of transportation fuels, lubes and other petrochemicals.
It is therefore an important object of this invention to convert more of the natural gas than just the dry gas portion to gasoline.
It is another object of this invention to convert natural gas to a wide slate of transportation fuels including gasoline, jet fuel and diesel fuel and petrochemical products including lubricating oil.
Other additional objects of this invention will become apparent from a consideration of this entire specification including the claims and the drawing hereof.